Diffusion vacuum pump



Nov. 28, ,-1967 v. oPoLsK DIFFUSION VACUUM PUMP Original Filed June 30, 1964 INVENTOR. Vcfav OpoS/g/ c l n United States Patent O DIFFUSHON VACUUM PUMP Vclav polslry, Prague, Czechoslovakia, assigner to Ceslroslovenska akademie ved, Prague, Czechoslovakia Continuation of application Ser. No. 379,304, .lune 30,

1964. This application July 11, 1966, Ser. No. 564,433

Claims priority, application Czechoslovakia, July 2, 1963,

3,806/63; Nov. 1, 1963, 6,015/63 4 Claims. (Cl. 230-101) This invention relates to vacuum pumps, and particularly to a vapor diffusion pump, this application being a continuation of my application Ser. No. 379,304, tiled .lune 30, 1964, now abandoned.

Diffusion pumps are made either of metal or of glass. Metal pumps require an insert of material having low heat conductivity to be interposed between the boiler and the diffuser to prevent excessive heating of the latter. This problem is less serious with glass pumps, Ibut their diffuser must still be air-cooled and provided with external metal fins which are difiicult to attach to the diffuser so that heat is transmitted efficiently.

The primary object of the invention is the provision of a vapor diffusion pump in which heat transfer from the boiler to the diffuser by conductance is held to a minimum.

Another object is the reduction of reverse diffusion of vapors in a direction from the diffuser toward the boiler to a minimum.

With these and other objects in view, the invention provides a pump of the type referred to in which a tubular diffuser member whose axis extends vertically in the normal operating condition of the pump is upwardly spaced from the boiler. An annular chamber has an upper annular portion which is radially outwardly spaced from an axially coextensive portion of the diffuser member, whereas the lower portion of the annular chamber axially connects the boiler with the diffuser member. The lower chamber portion communicates with the diffuser member and the boiler.

Connectors are provided for connecting the upper chamber portion to a space to be evacuated, and for connecting a portion of the diffuser member remote from the boiler with a forepump. A jet extends axially from the boiler toward the diffuser member and is partly axially coextensive with the lower chamber portion.

The exact nature of this invention, as well as other objects and advantages thereof, will be readily apparent from consideration of the following detailed specification relating to the annexed drawing in which:

FIG. 1 shows a vapor diffusion pump of the invention in elevational section; and

FIG. 2 shows the pump of FIG. l in plan section on the line Il-II.

The outer walls of the illustrated pump are mainly formed by a boiler 15 provided with a heating element 15 and filled to a level 15 with a suitable oil; by a vertical cylindrical tube 14 which mainly serves as a diffuser; and by an annular chamber 2 provided with a side tube 1 for connecting the pump to a receptacle to be evacuated. Another connector 12 at the upper end of the tube 14 permits the vapor pump to be connected to a forepump, such as a rotary pump. The tube 14 is covered with wire netting 16 and a wire spiral 16 for better air cooling.

A cover 9 upwardly closes the tube 14. A rod 4 extends axially downward from the cover 9 into the tube 14 and carries sets of three radial arms 3 at respective different levels to which jets or tubular vanes `5, 6, 7 are attached. The jets are coaxial and axially offset so that two axially adjacent jets define therebetween annular throats 8 of discharge nozzles. The arms 3 are axially adjustable on the rod 4 for securing the jets in different axial positions. The arms 3 are spaced far enough from the throats 8 not to interfere with vapor discharge.

Vapors from the oil in the boiler 15 are discharged upward from the jets 5, 6, 7. The vapors condense after they leave the throats 8, and the condensate descends along the inner wall of the tube 14 toward the boiler 15. The vacuum in the pump decreases from the lowermost jet 5 near the boiler 15 toward the jet 7 nearest the connector 12. Air is drawn from the side tube 1 into the vapor, and is carried by the vapor toward the connector 12.

A bafiie 9 which has the shape of an inverted funnel is integral with the cover 9', and the upper orifice of the jet 7 is received in the tubular funnel stem. The latter is provided with a radial bore 11 connecting the space in the stem with an annular condensation chamber 10 from which the connector 12 extends outward of the pump. The baffle 9 and the tube4 14 dene a narrow annular gap 10 which is normally filled by descending condensate, and prevents vapors from directly reaching the chamber 10.

The descending liquid film, which is partly saturated with air, meets the vapors vdischarged from the jets 6, 5 which expel the air particles from the liquid. The condensate ultimately reaching the boiler 15 is practically free of air.

The chamber 2 is shaped so as to present a large cooling surface to the ambient air. The upper annular portion of the chamber is spaced from the axially coextensive lowermost portion of the tube 14 in a radially outward direction. The lower portion of the chamber 2 axially connects the 'boiler 15 with the tube 14 and is radially open to the vertically elongated cavity of the pump which extends from the boiler to the top of the tube 14.

The bottom wall of the lower chamber portion 17 slopes conically downward toward the boiler 15. If any vapors should reach the chamber 2 by reverse diffusion, they lose their velocity in the radially enlarged portion of the pump cavity formed by the chamber 2, condense, and are guided by the -bottom wall of the chamber to an annular gap between the jet 5 and the boiler wall, and are returned to the boiler.

The tube 14 is covered externally with wire netting 16 which in turn is enveloped by a wire spiral 16 for more efiicient air cooling of the tube 14. However, the large surface of the chamber 2 is often sufcient for dissipating the entire heat conducted by the pump walls from the boiler 15, making it unnecessary to provide external cooling means on the tube 14. The tube 14 then is heated solely by the heat of condensation of the pumping fluid.

The advantages of the illustrate-d embodiments of the invention include countercurrent flow of vapors and condensate in the pump cavity which increases the pumping capacity. The lower portion 17 of the chamber 2 communicates with the pump cavity below the throat 8 of the lowermost jet 5, thereby making it unnecessary to provide a conventional vapor condenser which would decrease suction Velocity by 30 to 40 percent. The adjustable mounting of the jets permits the pump to be adjusted for different operating conditions, yet the arms 3 and the rod 4 do not disturb the proper aerodynamic properties of the pump. The chamber 2 dissipates most or all of the heat conducted away from the boiler 15, thereby avoiding the need for external cooling.

The pump of the invention may be constructed from metal or from glass, and is capable of attaining a vacuum of 5 106 mm. Hg in either case.

It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention, and that it is intended to cover all variations and modifications of the example of the invention chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

1. A diffusion vacuum pump comprising, in combination:

(a) a boiler;

(1b) a tubular diffuser member having an axis extending vertically in the operative condition of the pump and being upwardly spaced from said boiler in said condition;

(c) an annular chamber about said axis having an upper annular portion radially outwardly spaced from an axially coextensive portion of said diffuser member and a lower portion axially connecting said boiler to said diffuser member,

(1) respective walls of said upper portion and of said coextensive portion radially defining therebetween a space extending about said axis and being open to the atmosphere in said condition of the pump,

(2) said lower portion communicating with said boiler and said diffuser member;

(d) first connector means for connecting said upper portion to a space to be evacuated;

(e) second connector means for connecting a portion of said diffuser member remote from said chamber to a forepump; and

(f) a jet axially extending from said boiler toward said diffuser member and being partly axially coextensive with said lower portion.

2. A pump as set forth in claim 1, further comprising another jet axially offset from said first-mentioned jet and `defining an annular discharge nozzle therewith, and support means fastened to said diffuser member for securing said jets in each of a plurality of relative axial positions.

3. A pump as set forth in claim 2, wherein said support means -include a rod member axially extending in said diffuser member, said jets -being tubular about said axis, and the support means further comprisingr a plurality of radial arms connecting said jets to said rod member.

4. A pump as set forth in claim 1, further comprising another jet axially upwardly spaced from said first-mentioned jet and having an axially upwardly directed orifice, and a -bale member having the shape of an inverted funnel spacedly adjacent said other jet in an axial direction, said baffle member and said diffuser member defining an annular gap therebetween about said axis, and a condensation chamber above said gap, said second connector communicating with said condensation chamber, the condensation chamber being connected with the space within the funnel shape of said baffle member.

References Cited UNITED STATES PATENTS ROBERT M. WALKER, Primary Examiner. 

1. A DIFFUSION VACUUM PUMP COMPRISING, IN COMBINATION: (A) A BOULER; (B) A TUBULAR DIFFUSER MEMBER HAVING AN AXIS EXTENDING VERICALLY IN THE OPERATIVE CONDITION OF THE PUMP AND BEING UPWARDLY SPACED FROM SAID BOILER IN SAID CONDITION; (C) AN ANNULAR CHAMBER ABOUT SAID AXIS HAVING AN UPPER ANNULAR PORTION RADIALLY OUTWARDLY SPACED FROM AN AXIALLY COEXTENSIVE PORTION OF SAID DIFFUSER MEMBER AND A LOWER PORTION AXIALLY CONNECTING SAID BOILER TO SAID DIFFUSER MEMBER, (1) RESPECTIVE WALLS OF SAID UPPER PORTION AND OF SAID COEXTENSIVE PORTION RADIALLY DEFINING THEREBETWEEN A SPACE EXTENDING ABOUT SAID AXIS AND BEING OPEN TO THE ATMOSPHERE IN SAID CONDITION OF THE PUMP, (2) SAID LOWER PORTION COMMUNICATING WITH SAID BOILER AND SAID DIFFUSER MEMBER; 